OXYGEN ANALYZER

Abstract: The object of the invention is to provide an oxygen analyzer that has solved the various problems with the oxygen analysis of gases containing very small amounts of oxygen. The oxygen analyzer of the invention is suitable for use in the oxygen analysis of gases containing very small amounts of oxygen and features various improvements typified by a bypass pipe coupling between a pipe for gas supply to a detector and a pipe at gas outlet, a check valve provided halfway said bypass pipe, and means for detecting the pressure difference between said gas supply pipe and said gas outlet pipe.

Description: Technical Field This invention relates to an oxygen analyzer suitable for use in the oxygen analysis of gases containing very small amounts of oxygen, as described in US patent 4,973,935. It should be noted that the term "very small amounts" as used with oxygen in the specification refers to concentrations of no more than about 1 ppm. Background Art With the increasing scale of integration of semiconductor circuits, as well as the advances in the technology of ultrahigh precision working, it has become necessary to keep surveillance of the fabrication process, particularly for the oxygen concentration of the process gas which need be monitored over the range from the ppb to sub-ppb level. In such precision measurements, even the oxygen analyzers that have heretofore been used without any problems are found to cause various problems and need be improved. Among the problems that need be dealt with is the problem of dissolved oxygen in the water to be additionally supplied to the detector. It has been found that the results of measurements are affected by the presence of such small amounts of oxygen as have been insignificant to the conventional oxygen analyzers. Disclosure of the Invention It should be noted that the oxygen analyzer to be used in the invention is of a Hersch galvanic type and contains an aqueous solution (electrolyte) of a specified concentration range within a detector; the operating principle of the analyzer is such that the oxygen in a feed gas undergoes chemical reaction with the water in the electrolyte, whereby an electric current flows between electrodes in the electrolyte to permit the measurement of oxygen concentration. It should further be noted that the detector is capable of being supplied with a gas to be measured, a zero gas and a gain gas and these feed gases can be switched from one type to another by suitable means such as a valve. For the parts that are not particularly mentioned in the specification, any parts of and means in known oxygen analyzers may be applied. Brief Description of the Drawing Fig. 1 is a diagram of an oxygen analyzer of the invention that has an automatic water replenisher, as well as a device for purging a water tank as with an effluent gas from a detector. This invention provides an oxygen analyzer suitable for use in the oxygen analysis of gases containing concentrations of oxygen of no more than 1ppm and including a detector of the Hersch galvanic type, characterized in that the oxygen analyzer has a sensor for detecting the liquid level in the detector, a water tank, an outlet valve on said water tank which is in operatively association with said sensor and means for automatically replenishing the detector with water until it reaches a specified level, and further characterized by having a pipe conveying oxygen-free gas to the water in the water tank, a pipe conveying effluent gas from the detector to said water, and a pipe conveying part of the gas to be measured to said water such that dissolved oxygen in the water in the water tank can be eliminated. During measurements, water gradually evaporates from the electrolyte in the detector, so the level of the electrolyte in the detector decreases gradually. It is therefore necessary to perform occasional replenishments with water during measurements over an extended period of time. The oxygen analyzer of the invention enables automatic replenishment with water not only to avoid human errors during the replenishing operation but also to ensure optimal conditions of analysis by supplying additional water in an appropriate manner even in unattended operations such as at night. A gas to be measured, an effluent gas from the detector or an oxygen-free gas is introduced into the water tank and bubbling or some other means is employed to have these gases contacted with the water in the tank such that the dissolved oxygen in the water is removed. It is desirable that a pipe for supplying water from a water tank to a detector may be made of an oxygen impermeable material. The oxygen impermeable material to be used in the invention is preferably a metal. The invention is intended to ensure that the results of measurements will not be affected by the dissolved oxygen in the replenishing water. Stated more specifically, the water to be additionally supplied from the tank to the detector is ensured against dissolution of oxygen, by eliminating the dissolved oxygen in the water in the tank. It may also prevent the dissolution of aerial oxygen via the water supply pipe. In microanalysis of oxygen, the results of analysis will be affected even by the oxygen contained in the water being additionally supplied into the detector. Fig. 1 shows an example of the analyzer according to the invention. The detector is fitted with a liquid level detecting sensor and a valve in operative association with the sensor is provided halfway the pipe for supplying water from the water tank to the detector. The dashed lines represent the lines in which the gas to be measured, the effluent gas from the detector and the oxygen-free gas are respectively supplied to the water tank.

Claims: An oxygen analyzer suitable for use in the oxygen analysis of gases containing concentrations of oxygen of no more than 1ppm and including a detector of the Hersch galvanic type, characterized in that the oxygen analyzer has a sensor for detecting the liquid level in the detector, a water tank, an outlet valve on said water tank which is in operatively association with said sensor and means for automatically replenishing the detector with water until it reaches a specified level, and further characterized by having a pipe conveying oxygen-free gas to the water in the water tank, a pipe conveying effluent gas from the detector to said water, and a pipe conveying part of the gas to be measured to said water such that dissolved oxygen in the water in the water tank can be eliminated.

Inventors: MATSUMOTO YOSHIRO, TANAKA YOSHIYASU, MATSUMOTO, YOSHIRO, TANAKA, YOSHIYASU
Applicants: OSAKA OXYGEN IND, OSAKA SANSO KOGYO LIMITED
Application year: 1994
Main classification: G01N1
IPC codes: G01N33